Electrolytic deposition of thorium



March 18 1924. 1,487,174

J. W. MARDEN ET AL ELECTROLYTIC DEPOSITION OF THORIUM Filed July 51 1922UNVE T R JEZN 2 6 0/533 rHaMAs'RTHaM s- ATTORNEY deposition ofthoriumand more particularly ill - Patented Mar, 18,1924.

PICS;

JOHN WESLEY EN, or'msr cannon, Ann oan nnwaan com! THOMAS PHILIP THOMAS,013 BLOOMFIELD, NEW JERSEY, ASSIGNORS TO'T'ING- HOUSE LAMP COMPANY, ACOREORATION OI PENNSYLV l a ELECTROLYTIC nnrosr'rron or Tic-103mm.

Application and m 31, ieaa. Seriai n. 578,813.

To all whom it may concern."

Be it known that we J OHN WEsnnY MAR- DEN, JOHN EDWARD (JO'NLEY, andTHOMAS PHILIP ,THOMAS, citizens of the United States, and residents ofEast Orange, Bloomfield, and Bloomfield, respectively, in the county ofEssex and State of New Jersey, have invented a new and usefulImprovement in Electrol tic Deposition of Thorium, of which the folowing is a specification.

This invention relates to the electrolytic to the electroplating offilamentary material, electrodes and the like with metallic thorium forthe purpose of increasing the electronemissivity thereof.

An object of our invention is the forma-.

tion of a plating of thorium deposited from aqueous solution.

Another object of our invention is the production of thorium directly inmetallic for from aqueous solution thereof.

A further object of ouninvention is the preparation of metallic materialand other articles with a coating of thorium'metal deposited thereondirectly from aqueous'solufails to disclose a method for depositingthorium or thorium alloys, electrolytically from aqueous solutions..Moissan and Honigschmidt, Monatshaft fiir Chemie 27 ,685 (1906) andlater Von Wartenburgh, Zeit. Elektrochem. 15,866'( 1909) claimed to haveprepared impure thorium by the electrolysis of the fused double salt,sodium thorium chloride, (Na ThCI The metal thus obtained contains' atleast 15% of thorium oxide and the method was shown to be diflicult ofmanipulation. Heatingis necessary for the fusion of thesalt and theelectrolysis should be conducted 'in inert gas so that the metal may beas pure as possible. Such a method is obviously not very suitable forcoating or plating articles such as X-ray targets or filamentarymaterial for electron-emitting purposes.

According to our invention, we have devised a process whereby articlesmay be plated or coated electrolytically with thorium directly fromaqueous solutions thereof. The exact composition of the solution is notessential, the essence of the invention being the preparation of asolution of thorium which upon electrolysis thereof will .deposit acoherent and adherent coating of thorium or an alloy thereof so thatthe-'artiole or material coated therewith ma be used for electronemission, X-ray or 'ot er purposes in the same way in which solid metallic thorium could be used.

' One embodiment of our invention comprises dissolving thorium hydroxidein fluoboric acid. Although thorium hydroxide is only slightly solublein fluob'o'ric acid we have found that when some other compound,

' dry, oxygen-free, nitrogen, hydrogen oi";

such as lead hydroxide or carbonate, is

added, we are able-to deposit a mixture or alloy of the two metals fromsuch a solution.

Another embodiment of our invention comprises dissolving thoriumhydroxide in fluosilicic acid in the presence of a compound of lead suchas heretofore mentioned. Thorium and lead maybe depositedelectrolytically from such a solution in the same manner in which theyare deposited from a fiuo borate solution.

A further embodiment of our invention comprises preparing a solution bymixing.

neutral pptassium lactate with thorium chloride in t same manner asthelead'in a fluoborate or fluosilicate solution and deposits electrolgtically along with the thorium withthe e presence of ferrous chloride.-In such a solution the iron acts in much the,

mation of a coherent and adherent. coating-- on a suitable cathodeimmersed therein. This embodiment of our invention may be slightlymodified by substituting lead foriron, there by avoiding a slightconfusion that might arise if coated articles were used for*electron-emitting purposes because of the slight electron-emission ofiron.

. Although, a has heretofore been 0oIii(i' ered impossible to depositthorium electrolytically, it should be noted that lead alone has beendeposited or plated from fluosihcute and fiuoborate solutions andreference is made to the paper of W. Blum et al., Lead Plating fromFluoborate Solutions, published in vol. 36, pages 243 to 268 inclusive,of the Transactions of the American Electrochemical Society, 1919.

Our invention will better be understood by referring to the accompanyingdrawing which illustrates, partly in section and partlydiagrammatically, apparatus which may be used for coating wire orfilamentary material with thorium.

The tank 1, preferably coated on the inside with wax or some materialnot acted on by hydrofluoric acid, may be used for holding the platingsolution of thorium 2. The spool 3 may be wound with wire or filament =1of tungsten. or the like. which wire may be drawn through the solutionover pulley 5, rods or the like 6 and 7, of suitable material, pulley 8and wound up on spool or pulley 9. Any suitable mechanism may beemployed for driving the spool 9 at a uniformly slow rate of speed todraw the wire from the solution 2. An electrode 11 of carbon or the likeis inserted in the solution 2 and an electrical potential establishedbetween the electrode 11 as an anode and the filament as a cathode bymeans of battery 12 or other suitable source of direct current. Anammeter 13 and a rheostat 1 1 may be inserted in the circuit for thepurpose of indicating and adjusting the plating current to the desiredstrength.

Although only one end of the wire need be electrically connected to thebattery 12, it is preferable, especially where wire of small size andtherefore of high resistance is used, to connect the same to the batteryat points adjacent where the wire goes into and emerges from the platingsolution.

In the drawing, the wire is shown clectrically connected to the battery12 by means of conductors 15 and 16, respectively, connected to pulleys5 and 8 by means of which electrical contact is made with the wire to beplated. A switch 17 may be provided for making or breaking the circuitfrom the battery 12.

By means of the aforesaid apparatus, wire of tungsten or the like may beplated or electrolytically coated with thorium preferably. in the formof an alloy or mixture thereof, after first receiving a thin coating ofcopper or the like, which is preferably applied to make the coating ofthorium adhere more strongly to the wire. The thorium solution 2 may beprepared in any one of several ways,that is, it may be a fluoboratesolution of thorium in the presence of lead, a fluosilicate solution ofthorium meant in the presence of lead or a mixture of a lactate withsalts of thorium and iron or lead. A small amount of glue or othersuitable colloid is preferably added to the solution for the purpose ofmaking the deposit more firmly adherent to the wire or article beingplated.

An example of the formation of a plating solution by the fluoboratemethod may be as follows. Freshly precipitated thorium hydroxidetogether with a lead compound such as the hydroxide, carbonate or basiccarbonate is added to amixture of 32 grams of hydrofluoric acid (50%HF.)and 14.8 grams of boric acid (H BO Thorium hydroxide may be added wet sothat the resultant volume of the mixture is about 100 cubic centimeters.Some of the thorium added as hydroxide will precipitate as thoriumfluoride and should be filtered 0d and the clear liquid used.

In order that .an excessive amount of thorium fluoride will not beprecipitated, an excess of boric acid is preferably present in thesolution, over that needed to form fluoboric acid, and this excess alsotends to make the fluoboric acid more stable.

One-quarter gram of glue or other similar colloid, may then be added sothat the -elec-. trolytic deposit formed from the solution will becoherent and adherent. YVithout the glue the deposit is spongy andreadily falls off from the cathode. It is preferable that the article orwire to be coated with thorium is first coated or plated very thinlywith copper. With a copper sulphate solution containing 15% blue vitrioland 5% sulphuric acid. an exposure of about 1 or 2 minutes with acurrent density of about 10 to 50 milli-amperes per square centimeter ofcathode surface may be used. -The rate of deposit may easily be variedto suit conditions either by using other'concentration of electrolyte,time of deposition or current density.

A Wire of tungsten, for example, when copper plated as above described,which plating maybe performed with apparatus such as illustrated in theaccompanying drawing, may then be washed with water and placed in andpassed through the fluoborate solution prepared as heretofore describedwhere it is then plated with a mixture or alloy of thorium and lead bymeans of the apparatus hereinbefore described.

The time for depositing thorium may be varied according to the thicknessof the coating desired and the strength of the current used. A highercurrent density requires a shorter length of time but the deposit willnot adhere as well as when deposited more slowly. According to thismethod a 3 mil tungsten wire was increased insize to 4 mils, that is, ahalf mil coating was applied thereto, although thicker or thinnerdeposits maybe made to uit the need. Such a wire, when used as a hotcathode in suitable electron emission apparatus, the gas therein beingremoved by suitable well known means, showed the characteristicelectromemission of thorium. A few readings of this wire are given hereto verify this statement.

At 10 :30 a. m. an emission of 77 milliamperes Per square centimeter ofwire surface at about 1780 K. was obtained, on continuous service at 3p. m. an emission of milliamperes per square centimeter was obtained atabout 1765 K.; while at 4.45 p. In. another reading showed 77milliamperes per square centimeter at about 1780 K. (absolute). v

Thorium in the presence of lead may also be electroplated or de ositedfrom a fluosilicate solution prepare in a similar manner to thatdescribed for a fiuoborate solution. It is to be understood that we donot restrict ourselves to the use of lead as a co-precipitator forcausing thorium to deposit, for there are other metals as well, which wecontemplate using, such as iron, nickel, copper and many others. Thereason lead has been used to aid in the deposition of the thorium, is onaccount of the low electron-emission of lead and its oxide.

A tungsten wire, as above described, plated with lead alone will give noindication of electron-emission in any stage of its heating. The onlyemission observed from the mixture then is that of thorium alone, at anypoint below the emission temperature of tungsten.

Another method for successfully depositing or electroplating withthorium is that using a lactate solution, for example, a thoriumironmixture or alloy may be de posited from a solution of the followingcomposition using the same conditions regarding current density, anodeand cathode surface as hereinbefore described with reference tofiuoborate solutions.

First it is preferable to neutralize to litmus 79.; grams of 85% (U. S.P.) lactic acid with a strong solution (50%) of potassium hydroxide. Afew cubic centimeters of a solution which contains 1.3 grams of thoriumchloride and a few cubic centimeters of a solution of ferrous chlorideand 2 grams of potassium chloride may then be added. The total volume ofthe solution is then preferably made up to 100 cubic centimeters and 5drops of lactic acid added to acidify it slightly. When electrolyzedunder the same conditions as heretofore described for a fluoboratesolution, a gray-white deposit consisting of an alloy or mixture of.thorium and iron may be obtained, which adheres well to the article orwire plated and may Such a de osit is less crystalline and moredescribed. A filament coated with a thorium-lead alloy or mixture by thelactate method when tested showed electron emission of 48 milliamperesper square centimeter of filament surface at about 1730 K.

It will be apparent that our invention may be used for many purposes,for example, the electron-emission of many elements may be determined byelectroplating on a filament from a solutionand testing theelectronemission of theplated filament. In this way theelectron-emission of elements which have not yet been prepared inmetallic form may be determined. We also have in mind the deposition ofcalcium, strontium and barium alloys and the subsequent oxidation ofthese for oxide-coated filaments for radio bulbs and the like. We alsohave in mind the dep osition of pure metals which have not yet beenprepared in this way from various aqueous solutions and some of whichhave never been prepared at all. With some of these materials, we mayfind it more desirable to plate from glycerine or alcoholic solutions orto use other salts than those here tofore mentioned. I

According to our invention a mixture or alloy of a metal may bedeposited with a more volatile one and the latter volatilized leavingthe pure metal, or possibly the reverse method, to recover the desiredmetal plated as a mixture or alloy by distilling and condensing the sameon a cold surface.

Although we hate described what we now consider'to be the preferredmeans of practicing our invention and have described specificembodiments thereof, it is to be understood that the same are merelyillustrative and that our invention is limited only by the scope andspirit of the appended I c aims.

What is claimed is:

1. The method of forming thorium metal comprising preparing a solutionthereof and depositing thorium therefrom electrolytically.

2. The method of preparing metallic thorium comprising forming anaqueous solution of a salt thereof and decomposing the same byelectricity to deposit thorium therefrom.

3. The method of electroplating with thorium comprising dissolving acompound be made up to a considerable thicxness. thereof and passing acurrent between an "anode and a cathode in the solution formed,

d. The method of forming thorium metal comprising preparing a solutionof a thorium compound in water and decomposing said compound by passingelectricity between an anode and cathode therein, whereby a coating ofthorium is deposited on the cathode.

5. The method of coating with thorium comprising dissolving thoriumhydroxide and inserting the material to be coated in the solution soformed as a cathode and depositing thorium thereon by electricity.

6. The method of electro-depositi-ng thorium comprising preparing afluoborate solution thereof in the presence of lead and inserting thematerial desired to be plated in said solution as a cathode andimpressing a potential between the same and an anode of any suitablematerial such as carbon.

7. The method of coating material with thorium comprising perparing afluosilicate solution of thorium and lead, inserting the material to becoated therein and depositing thorium thereon electrolytically.

8. The method of electroplating material with thorium comprisingdissolving salts of thorium and iron in a lactate solution and insertingthe material to be coated with thorium as a cathode therein.

9. The method of electro-depositing thorium comprising dissolving saltsof thorium and lead in an acidified lactate solution and insertingmaterial to be coated with thorium as a cathode (therein.

10. The method of coating a wire continuously with thorium comprisingpassing -it slowly through a fluoborate solution of thorium and leadwhile maintaining a potential between said wire as a cathode and ananode of any suitable material not attacked by the solution.

11. The method of continuously coating filamentary material or the likewith a thorium alloy or mixture comprising preparing a solution ofthorium and another metal and passing the material through said solutionwhile maintaining a potential between the same as a cathode and asuitable anode immersed in said solution.

12. The method of plating metallic material with thorium comprisingdissolving item's-*4.

a suitable anode and rent therebetween.

14. The method of plating metallic material with thorium comprisingdissolving thorium hydroxide and lead hydroxide or the like influosilicic acid, inserting the material therein as a cathode with asuitable anode and passing electric current therebetween.

15. The method of plating metallic material with thorium comprisingdissolving thorium chloride and ferrous chloride in a solution ofpotassium lactate or the like, inserting the material therein as acathode with a suitable anode and passing electric current therebtween.

16. The method of plating metallic material with thorium comprisingdissolving thorium chloride and ferrous chloride in a solution ofpotassium lactate, acidulating it slightly with lactic acid, providingthe metallic material with a surface of cop per, insertin it in thesolution as a cathode with a suita le anode and passing electric currenttherebetween.

17. Filamentary material for electronemitting purposes comprisingtungsten or the like electroplated with thorium.

18. An X-ray target electroplated with thorium.

19. Electron-emission material comprising a refractory metal, coppercoated, upon which thorium has been electroplated.

20. Electron-emission material comprising tungsten or the like copperplated and then electroplated with an alloy of thorium.

21. Electron-emission material comprising molybdenum or the like, copperplated and electroplated with an alloy or mixture of thorium and iron.

22. Metallic material plated with an alloy or mixture of thorium andanother metal.

23. Metallic material plated with copper and then electroplated withthorium.

24. Metallic material plated with copper and then electroplated with analloy or mixture of thorium and lead. I

25. Copper plated metallic material electroplated with an alloy ormixture of thorium and iron. I

26. An X-ray target formed of refractory metal electroplated withthorium and another metal.

27. An X-ray target formed of tungsten or the like electroplated withthorium and another metal. r

28. An X-ray target formed of tungsten copper-plated and thenelectroplated with thorium and another metal.

29. An X-ray target formed of tungsten or the like electroplated withthorium.

30. An X-ray'target formed of refractory metal electroplated withthorium and lead.

31. An X-ray target formed of refracpassing electric our- Mill torymetal electroplated with thorium and Iron.

32. An X-ray target formed of refractory metal copper-plated andelectroplated with thorium.

33. An X-ray target formed of tungsten or the like copper-plated andthen electroplated with an alloy or mixture of thorium.

34. An X-ray target formed of tungsten or the like copper-plated andthen electroplated with an alloy or mixture of thorium and anothermetal.

35. An X-ray target comprising refractory metal copper-plated and thenelectroplated with an alloy or-mixture of thorium 15 and lead.

36. An X-ray target formed of tungsten or the like plated with copperand then electroplated with an alloy or mixture of thorium and iron.

37. An X-ray target coated with thorium.

In testimony whereof, we have hereunto subscribed our names this 28thday of J uly 1922.

JOHN WESLEY MARDEN. JOHN EDWARD CONLEY. THOMAS PHILIP THOMAS.

